title: G-protein coupled receptor 56 promotes myoblast fusion through serum response factor- and nuclear factor of activated T-cell-mediated signalling but is not essential for muscle development in vivo.
abstract: Mammalian muscle cell differentiation is a complex process of multiple steps for which many of the factors involved have not yet been defined. In a screen to identify the regulators of myogenic cell fusion, we found that the gene for G-protein coupled receptor 56 (GPR56) was transiently up-regulated during the early fusion of human myoblasts. Human mutations in the gene for GPR56 cause the disease bilateral frontoparietal polymicrogyria; however, the consequences of receptor dysfunction on muscle development have not been explored. Using knockout mice, we defined the role of GPR56 in skeletal muscle. GPR56(-/-) myoblasts have decreased fusion and smaller myotube sizes in culture. In addition, a loss of GPR56 expression in muscle cells results in decreases or delays in the expression of myogenic differentiation 1, myogenin and nuclear factor of activated T-cell (NFAT)c2. Our data suggest that these abnormalities result from decreased GPR56-mediated serum response element and NFAT signalling. Despite these changes, no overt differences in phenotype were identified in the muscle of GPR56 knockout mice, which presented only a mild but statistically significant elevation of serum creatine kinase compared to wild-type. In agreement with these findings, clinical data from 13 bilateral frontoparietal polymicrogyria patients revealed mild serum creatine kinase increase in only two patients. In summary, targeted disruption of GPR56 in mice results in myoblast abnormalities. The absence of a severe muscle phenotype in GPR56 knockout mice and human patients suggests that other factors may compensate for the lack of this G-protein coupled receptor during muscle development and that the motor delay observed in these patients is likely not a result of primary muscle abnormalities.
authors.affiliation: Department of Biological and Biomedical Sciences, Harvard Medical School, Boston, MA, USA; Division of Genetics, Boston Children's Hospital, MA, USA.
authors.forename: Melissa P
authors.initials: MP
authors.lastname: Wu
authors.forename: Jamie R
authors.initials: JR
authors.lastname: Doyle
authors.forename: Brenda
authors.initials: B
authors.lastname: Barry
authors.forename: Ariane
authors.initials: A
authors.lastname: Beauvais
authors.forename: Anete
authors.initials: A
authors.lastname: Rozkalne
authors.forename: Xianhua
authors.initials: X
authors.lastname: Piao
authors.forename: Michael W
authors.initials: MW
authors.lastname: Lawlor
authors.forename: Alan S
authors.initials: AS
authors.lastname: Kopin
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Walsh
authors.forename: Emanuela
authors.initials: E
authors.lastname: Gussoni
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002450:Cell Communication; D002454:Cell Differentiation; D002459:Cell Fusion; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D007124:Immunoenzyme Techniques; D008156:Luciferases / Q000378:metabolism; D008297:Male; D054220:Malformations of Cortical Development / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D018345:Mice, Knockout; D024510:Muscle Development / Q000502:physiology*; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D032446:Myoblasts / Q000166:cytology* / Q000378:metabolism; D018008:Myogenin / Q000235:genetics / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D043562:Receptors, G-Protein-Coupled / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027602:Serum Response Element / Q000235:genetics*; D015398:Signal Transduction
chemical_list: D008156:Luciferases; D017570:MyoD Protein; D018008:Myogenin; D050778:NFATC Transcription Factors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled; C524781:Adgrg1 protein, mouse; C057363:MyoD1 myogenic differentiation protein
keywords: GPR56; dystroglycanopathies; myoblast; serum response element; skeletal muscle